Here is a facimile of Joseph Moxon's original instructions for chopping a mortise. It comes from
his serialized magazine, Mechanick Exercises, the first woodworking instructions ever published in English.
This section, originally published in May of 1678, describes a method that includes chopping the mortise
slightly small and then paring to the scribe lines. Moxon's technique does not appear in any 19th or 20th
century instruction that we know about. Nevertheless, it is the method I was taught. -Joel